Computer viruses are known in the art and represent one form of computer disease. Viruses are essentially computer programs that have the ability of infecting the memory of computer systems, deleting or augmenting that memory, as well as being able to replicate themselves via use of communication lines or portable memory such as floppy disks. It has been found that most computer viruses are transmitted either in the sale of new floppy disks, or through the swapping of floppy disks, and by the interconnection of computers using modems and networks. If a computer system becomes infected with a computer virus, the user has the option of purchasing software that is able to identify the virus, so that the infection can be eradicated. In such a process, it is required to establish the viral "fingerprint" which gives the computer user an indication as to how the virus works and how to prepare software that will actually combat the viral fingerprint. However, in destroying the virus, it is sometimes possible to destroy program data as well.
However, to establish a viral fingerprint through the loading of appropriate software, it is necessary, in personal computers, for the disk operating system (DOS) to be operating which also allows the computer virus to operate. It has been found, that some computer viruses actually attack the software attempting to establish the viral fingerprint.
At the date of this application, there are approximately 1600 viruses present throughout the world. One software manufacturer has established 475 viral fingerprints and it will be apparent to those skilled in the art, therefore, that many computer viruses cannot be effectively treated.
Many computer viruses are particularly intelligent and one such virus, named STONE, has been identified as being able to be changed by human re-enginerring so as to alter its viral fingerprint. At present, the STONE virus is also known in two mutated forms, STONE I and STONE II. There are many self-mutating (stealth) viruses, such as "1260", "V800" and "DARK AVENGER" strains. Another intelligent virus is known as FRIDAY THE 13TH and, as implied by its name, this virus only becomes active on that particular date. Such an operation is readily available as most computer systems include a CMOS real-time clock which the intelligent virus can monitor and enable itself on a particular day.
Other forms of computer "disease" take the form of "Trojans", "worms" and "logic bombs". Trojans and logic bombs have the effect of infecting a computer system, sometimes under the guise of something else (as in the Trojan Horse), and "exploding" in such a manner that blocks of data stored in memory are destroyed irretrievably. As their names imply, they have a once-only function. Worms have the effect of infiltrating many memory locations in a computer system and generally cause nuisance effects.
For convenience, throughout this specification computer viruses, worms, trojans, logic bombs, and the like, are grouped together as "diseases", but where applicable, references made to "viruses", because of that terms acceptance in the art, are to be considered references to "diseases" in general.
It is an object of the present invention to substantially overcome, or ameliorate the above mentioned difficulties through provision of a means by which actual damage caused by computer diseases, can be prevented. It will be apparent to those skilled in the art that disease infection of a computer system is generally not preventable, as the disease software is merely data and, when read from a floppy disk or via a network, the computer system sees the disease as merely one small section of data within an entire data transfer.